Conventionally, an electromagnetic flow amount control valve (electromagnetic valve) is put forth that is provided with: a housing that has a cylindrical valve seat in which a fluid passage hole is formed; a valve element that is lifted off and seated on the valve seat to open and close the fluid passage hole; a coil that generates magnetomotive force when it is energized; a fixed core that is magnetized by the magnetomotive force of the coil; an electromagnetic driving portion provided with a moving core that is magnetized by the magnetomotive force of the coil to be attracted toward an attracting portion of the fixed core (to one side in an axial direction); and a valve shaft that links an operation of the valve element with an axial reciprocating motion of the moving core of the electromagnetic driving portion. The electromagnetic valve is generally configured so that moving elements (the moving core, the valve shaft and the valve element) moves to the one side in the axial direction until they come in contact with a stopper that is provided in the fixed core when the magnetomotive force of the coil attracts the moving core toward the attracting portion of the fixed core. In the electromagnetic valve, when the coil stops being energized and the magnetomotive force extinguishes, an urging force of a spring, which is provided in the electromagnetic driving portion, pushes the moving elements backward to the other side in the axial direction to seat the valve element on the valve seat of the housing.
Accordingly, the electromagnetic valve has such an issue that the moving core and the valve element generate operational noises of when the moving elements come in contact with the stopper or the valve seat in both a valve-opening operation time and a valve-closing operation time. In this regard, U.S. Pat. No. 6,581,904-B2, for example, discloses a method to reduce the operational noise of the electromagnetic valve by using a damper effect. In this method, a fitting portion of a diaphragm, which is formed from thin elastic body, is fixed to an outer circumference of the valve shaft, and a radially outer end portion of the diaphragm is supported by being sandwiched between the housing and an end face of the electromagnetic driving portion. Thus, an inner space of the housing, which is formed between the end face of the electromagnetic driving portion and the valve seat of the housing, is airtightly partitioned into a first pressure chamber at a side of the valve seat of the hosing and a second pressure chamber at a side of the electromagnetic driving portion. The first pressure chamber has a construction to flow control fluid therethrough, and the second pressure chamber is filled with gas.
In the valve-opening operation time of the electromagnetic valve, the gas in the second pressure chamber, which is pressurized in accordance with a shrinkage of the diaphragm, is subjected to a passage resistance in passing from the second pressure chamber through an orifice that is provided at the side of the electromagnetic driving portion. Thus, the damper effect by the passage resistance decreases a traveling speed of the moving core to the one side in the axial direction, to reduce the operational noise of the electromagnetic valve due to the moving core coming in contact with the stopper. Further, in the valve-closing operation time of the electromagnetic valve, the damper effect by the passage resistance decreases the traveling speed of the moving core to the other side in the axial direction, to reduce the operational noise of the electromagnetic valve due to the valve element seating on the valve seat of the housing.
It is considered to apply the electromagnetic valve according to U.S. Pat. No. 6,581,904-B2 to an electromagnetic valve that is subjected to both the positive pressure and the negative pressure acting on an outer surface of an elastically deforming portion of the diaphragm. In this case, the elastically deforming portion is alternately deformed into a protruding shape and into a depressed shape by the alternate positive and negative pressures acting on the outer surface of the elastically deforming portion of the diaphragm. Thus, the durability of the elastically deforming portion decreases, so that a crack may generate on the diaphragm to tear the diaphragm. It is considered to increase the thickness of the elastically deforming portion of the diaphragm to prevent the degradation and the breakage of the elastically deforming portion that is incorporated in the electromagnetic valve. However, the hard elastically deforming portion is not easily deformed, to decrease a control response performance of the electromagnetic valve. It is also considered to increase a radius of the elastically deforming portion, however, the dimensions of the housing must be changed in accordance with the upsizing of the diaphragm, and this decreases the mountability of the electromagnetic valve in an engine room of the vehicle and the like.
In this regard, JP-2000-018399-A, for example, discloses an electromagnetic valve provided with a bellows (bellowphragm) that can be used in both the positive and negative pressures. The bellows of this electromagnetic valve has a cylindrical bellows portion that surrounds the valve shaft. A motion of the cylindrical bellows portion is linked with the axial reciprocating motion of the moving core of the electromagnetic driving portion, so that the cylindrical bellows portion extends and shrinks in the axial direction in accordance with the axial reciprocating motion of the moving core of the electromagnetic valve. One end of the bellows in the axial direction of the valve shaft, which is at the side of the electromagnetic driving portion, is opened, and the other end of the bellows in the axial direction of the valve shaft, which is at the side of the valve seat of the housing, is closed. A valve element is integrally provided in the closed portion at the other end of the bellows, to be seated on and lifted off the valve seat of the housing to close and open the valve hole. A communication passage is formed in the valve element to communicate an inner space of the cylindrical bellows portion of the bellows with an outer space of the cylindrical bellows portion, that is, with a fluid passage at an upstream side than the valve seat of the housing.
Accordingly, the bellows in this conventional electromagnetic valve has such a construction that a total volume in a plurality of partitioned spaces, which increases and decreases in accordance with the extending and the shrinking operations of the cylindrical bellows portion, is quite small relative to the whole volume in the inner space in the cylindrical bellows portion that is formed between an inner circumferential face of the cylindrical bellows portion and an outer circumferential face of the valve shaft. Thus, when the cylindrical bellows portion of the bellows shrinks in accordance with a displacement of the moving core and the valve shaft to the one side in the axial direction, the fluid filled in the inner space of the cylindrical bellows portion is discharged at a stroke through the communication passage to the side of the fluid passage, to cause an issue that the electromagnetic valve does not generate enough damper effect as in the above-mentioned electromagnetic valve provided with the diaphragm.